1. Field of the Invention
The invention relates to an optoelectronic device and more particularly to an image sensor device using a submicron structure.
2. Description of the Related Art
As optoelectronic devices become more and more popular, such as digital camera, digital video recorder, image capture cap able mobile phone and monitor, demand for image sensor devices accordingly increase. An image sensor device is used to record and change a photo signal from an image to an electronic signal. After recording and processing the electronic signal, a digital image is generated. In general, image sensor devices can be categorized into two main types, one is charge coupled devices (CCD) and the other complementary metal oxide semiconductor (CMOS) devices.
In order to improve image sensor device performance, laterally integrated CMOS image sensor devices, which use CMOS circuitry in each pixel and photodiodes for light sensing devices, have been developed. The CMOS circuitry increases sensitivity and reduces noise, allowing pixel size to shrink while maintaining functionality. For a typical laterally integrated CMOS image sensor device, the photodiode and the CMOS circuitry are formed next to each other on a silicon substrate. Thus, fill factor is reduced, lowering the sensitivity of sensors. If pixel size increases to maintain sensitivity, resolution will be reduced.
U.S. Pat. No. 6,709,885 discloses an image sensor device fabricated by vertically integrating a photodiode above the CMOS control circuitry to increase fill factor. Accordingly, such an image sensor device can provide higher sensitivity with the same pixel size as the laterally integrated CMOS image sensor device.
However, as the pixel size is reduced in order to form more pixels to increase resolution, the fill factor is reduced and results in an increase in the dark current due to increased dead zones between pixels, thus aggravating image lag effect. The dead zone of the photodiode is a region where the transfer efficiency of optical charges is poor and dark current is generated due to thermal generation of charge carriers, thus no signal is generated at the dead zone when light enters the photodiode.
Therefore, there is a need to develop a novel image sensor device structure capable of alleviating image lag effect by reducing dark current in the image sensor device.